1. Field of the Invention
The invention refers to a process for connecting frogs consisting of austenitic manganese steel casting with rails consisting of carbon steel by aluminothermic welding.
2. Description of the Prior Art
Austenitic manganese steel castings are, on account of the excellent wear resistance of such steels, the most frequently used materials for the frogs of crossings or switches in railroad construction. The rails used in railroad construction consist, as a rule, of carbon steel and direct welding of such carbon steels with austenitic manganese steel castings is not easily possible on account of the different temperature treatment of the work pieces to be connected one with the other. For this reason, frogs consisting of austenitic manganese steel castings are at present connected with the connecting rails by means of fishplates or, prior to moving the track, the frogs consisting of austenitic manganese steel casting are welded by using an intermediate piece of low carbon austenitic steel with a connecting rail consisting of carbon steel which connecting rail can then be welded in the track with the connecting rail. In case of fracture of this connection the frog must be dismounted for welding thereto a new intermediate piece and the connecting rail. It is already further known to make the welding connection by aluminothermic welding, noting that also in this case a perfect connection can not easily be obtained. The reason therefor is, that martensite is formed on subsequent cooling on account of the diffusion processes taking place during welding within the austenitic manganese steel in the connecting zone. Such formation of martensite could only be avoided by an extremely slow cooling.
Carbide precipitations could, however, occur in the heat-influenced zone of the austenitic manganese steel on slow cooling, which would equally detract from the toughness.
From AT-PS No. 350 881 there has become known a process for connecting frogs consisting of austenitic manganese steel casting with rails consisting of carbon steel, according to which an intermediate piece having a maximum length of 20 to 25 mm and consisting of a low carbon austenitic steel is welded with the frog consisting of austenitic manganese steel casting. Cooling of this welding connection is effected relatively slow as compared with the cooling effected after the subsequent welding of the intermeidate piece with the connecting rail. For making such a welding connection there was thus required a plurality of subsequent process steps, each of which required precise control of the individual process parameters.
It is already further known to make the welding connection by aluminothermic welding. For this purpose, in AT-PS No. 374 720 an aluminothermically formed steel welded connection has been proposed which is substantially free of phosphorous and silicon and having a carbon content between 0.75 and 0.95 percent by weight. By means of such an aluminothermic melt, carbide precipitations can not reliably be prevented, which might detract from the toughness.